The manufacturing of integrated circuits involves a plurality of process steps, in which a plurality of chemicals/materials is involved. Some of these chemicals are liquids. For example, the manufacturing of a chip may include many photolithography steps. In each of the photolithography steps, photo resists, Bottom Anti-Reflective Coating (BARC), and the like, are often used.
To improve the manufacturing yield, the chemicals may be filtered, so that the undesirable substances and particles in these chemicals may be removed before the chemicals are used in the manufacturing of integrated circuits. The filtering is performed using membranes, wherein the chemicals penetrate through the pores of the membranes, while the undesirable substances and particles, which have sizes greater than the pore sizes, are blocked. Since the membranes used for holding the membranes may contain undesirable impurities and chemicals themselves, the membranes need to be cleaned first before they are used, otherwise, the membranes become the source in contaminating the chemicals that are cleaned.